[Diy_efi] DIY-WB construction & testing... help

[rr]

Andrew Brownsword wrote:
> 
> >>on 7/18/02 2:27 PM, rr at RRauscher at nni.com wrote:
> 
> Thanks for responding in my time of need.   :)
> 
> >> The UEGO circuit fails two tests:  pin 5 of U3 measures 7.2v instead of 7.8
> >> - 8.0, and J5 measures 1.8v instead of 1.9 - 2.1.
> >
> > For U3 pin 5 lift one leg of the cap C12 and re-measure. IF the voltage
> > goes up that cap is leaky.
> 
> The voltage didn't change, so the capacitor would seem to not be the
> culprit.  Any other suggestions?  Is it related to the J5 voltage problem?

Have you cleaned the flux off the board yet?

> 
> > J5 should really be closer to 2 volts. Is the +4 volt (VGnd) measurement
> > on the low side? This would contribute to a low J5 reading. If not then
> > double check the resistors R31, R32 & R35; as to being 1% to and 10K &
> > 100K.
> 
> The VGnd voltage is about 3.95v -- so it is on the low side.  Could this be
> a result of my power supply being on the 12.5v?  Does it matter?  Those 3
> resistors are all very close to their target values (<0.5% error).

3.95v is at 1.25%, darn good. Lets see, 1.8v/2.0v = 10%. That is why I
believe it should be higher. Maybe check the specs on the DVM you are
using. It may be loading the circuit.

> 
> >> When I power on the heater circuit the LED doesn't come on.  The site says I
> >> need 13-16 volts and the (R/C model) battery I'm using is only 12.5v -- is
> >> this likely the reason?  When I measure the voltage across the LED it seems
> >> to read -11.5v which makes me wonder if I put the LED on backwards, but I've
> >> got the flat spot opposite the stripe on the PCB which is how the
> >> construction guide indicates it should be.
> >
> > If this is w/o the sensor or any load connected then the 12 V is enough
> > to light the LED. Hmm, I thought that the flat went w/the stripe. Let'me
> > check. . . Yes, the board I looked at has the LED flat on the same side
> > as the footprint stripe end.
> 
> I reversed it and now it works fine.  I had it backward because this page
> http://www.aces.edu/~gparmer/efi/temp/wb/guide.html says:
> 
> "The cathode (+) is identified by end having the stripe , a "+" marking, or
> a longer lead. Also notable is that the LED has a flat spot machined on side
> of the lens corresponding to the anode (-). On the schematic, the cathode is
> the base of the triangle and the anode is the straight bar with the triangle
> pointing at it. Notice that the cathode (+) being identified by a stripe is
> a theme repeated on the circuit board (even for diodes like the LED which
> are not identified this way). If the leads have already been cut on your
> LED, look inside the diode. You'll notice two hunks of metal. The larger is
> the anode."
> 
> Which, as I read it anyhow, implies that the flat spot is anode and the
> stripe is cathode... meaning that the flat spot is away from the stripe.
> What am I missing?
> 
> 
> > P.S. note that the checks #34+ are not entirely valid. If they work OK,
> > If not then do not worry about it.
> 
> I'm following this:  http://www.diy-wb.com/diywbchk.htm  and my browser
> doesn't show any sensible test numbers... which one is #34, and should I
> even bother trying them if they aren't entirely valid?  Hooking up the
> switch sounds like a bit of a pain.
> 

You can try the tests, if they wwork good. If not, then do not worry 
about it. Step 34 starts with:

     Keeping the DVM on U2 pin 8 close the switch. The voltage will 
     slowly drop. It will take ~ 2 minutes with the voltage
     reaching ~ -3.4 v. 
           If not check C10, R18, R34 and U2. 


BobR.

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